Float actuated devices for monitoring liquid level and activating switch contacts at predetermined liquid level thresholds.
A float liquid level switch is an instrument for monitoring the height of a liquid and tripping an electrical contact switch when a maximum, minimum or intermediate level has been reached. The liquid level switch output can then be utilised by other instrumentation to open a valve, illuminate a warning lamp, activate an audible alarm, or switch on a pump.
Float liquid level switches are threshold contact trip devices which typically consist of a buoyancy component which is typically a sealed hollow ball or cylinder which will float on a liquid, and either a shaft assembly for vertical mounting, or a hinge mechanism for horizontal mounting.
As the level increases and decreases a float will be pushed up or drop down. The float can be connected to a hinge that opens and closes or slides along a shaft.
The position of the float along the shaft or the opening and closing of the hinge can be detected by various means.
A vertical mount sliding float type level switch will have a permanent magnet incorporated into the float which slides up and down the shaft. A magnetic reed switch is positioned along the shaft to the required level set point. When the float pashes over the reed switch it will open or close the level switch circuit.
A horizontal mount hinged type float level switch will incorporate either a microswitch or a magnetic reed switch, which is activated by an actuator or lever connected to the float.
It is possible to fit more than one switch to shaft type float switch, and provide liquid level control for a number of separate processes which are activated at different levels.
A float level switch makes direct contact with the liquid to be measured, and therefore material compatibility must be considered.
Since there are no pressure sensitive components exposed to the inside of the tank it is possible to fit float level switches to sealed pressurised tanks.
Float liquid level switches can be designed to mount through the top, side or bottom of a tank. Side entry type float level switches have hinged floats, and top and bottom entry type float level switches have sliding floats.
- Different types available for top, side or bottom entry mounting
- Cheapest type of liquid level switch
- Simple design and construction
- Not sensitive to changes in SG & density
- Some types do not require power to operate
- Surface disturbances such as ripples, foaming and bubbling will not affect performance
- Dielectric constant or conductivity of fluid will not affect operation
- Different materials for media compatibility can be specified
- Vapours, condensation and mists will not affect operation
- Vacuum and low pressure sealed tank will not compromise buoyancy of float
- Moving parts vulnerable to clogging, wear and tear, and damage
- Fouling can cause unreliable movement or seizure of float actuation
- Float actuation relies on liquid contact
- Turbulence in the fluid may cause the float to move
- Thick or sticky fluids may prevent the float from moving
- Regular maintenance to ensure nothing is restricting float movement
- Single point level switch with side entry type
- Float assembly protruding into liquid causing obstruction, attracting fouling and hygienic cleanliness issues